Method for forming an alignment layer of a liquid crystal display device and display device manufactured thereby

ABSTRACT

A novel method of forming an alignment layer of a liquid crystal display device includes the steps of providing a substrate (e.g., a processed silicon wafer, etc.) having an alignment layer material deposited thereon and applying a series of pulses from a pulse laser to anneal portions of the alignment layer material and alter its surface morphology. The method can include the step of depositing the alignment layer material (e.g., a spin-on dielectric including SiO 2 ) over the substrate using a spin-on process prior to laser annealing. Applying the series of laser pulses creates a repetitive pattern of features that facilitate alignment of liquid crystals according to a laser scan trace. Liquid crystal display devices with laser-annealed alignment layer(s) are also disclosed. The alignment layers of the invention are quickly and inexpensively applied and are very robust under prolonged, high-intensity light stress.

BACKGROUND Field of the Invention

This invention relates generally to liquid crystal display (LCD) devicesand methods of manufacturing them. Even more particularly the inventionrelates to methods for forming alignment layers used in LCD displays.

Description of the Background Art

Reflective and transmissive LCD devices are used in video projectors,rear projection televisions, computer displays, and other devices as ameans for producing high-quality imagery. FIG. 1 shows a known liquidcrystal display device 100, which in this embodiment, is a reflectiveliquid crystal on silicon (LCOS) light valve. Display device 100 isformed on a silicon substrate 102, and includes integrated circuitry104, an insulating layer 106, a plurality of pixel mirrors 108, aplanarized layer 110, a protective coating 112, a lower liquid crystalalignment layer 114, a liquid crystal layer 116, an upper liquid crystalalignment layer 118, a transparent electrode layer 120, a transparent(e.g., glass) substrate 122, and an anti-reflective coating 124. Thethicknesses of the layers depicted in FIG. 1 are not shown to scale, butare instead are drawn to be clearly visible.

Mirrors 108 are coupled to circuitry layer 104 through a plurality ofvias formed in insulating layer 106. Planar layer 110 and protectivelayer 112 provide a flat, relatively robust surface for subsequentlayers of the device. Alignment layers 114 and 118 help to properlyalign the liquid crystals of layer 116. Transparent electrode 120 (e.g.,Indium Tin Oxide) and antireflective coating 124 are formed on thebottom and top surfaces, respectively, of glass substrate 122. Alignmentlayer 118 is formed on transparent electrode 120.

During operation, light passes through all of upper layers 124, 122,120, 118, 116, 114, 112, and 110 of display device 100 to impinge onpixel mirrors 108. The light is reflected from the top surfaces ofmirrors 108 and then exits the device again passing through upper layers110, 112, 114, 116, 118, 120, 122, and 124. The polarization of thelight is altered by liquid crystal layer 116, depending on theelectrical field applied across liquid crystal layer 116. Whentransparent electrode 120 is held at a particular voltage, theelectrical field across liquid crystal layer 116 is controlled by thevoltages asserted on pixel mirrors 108 by circuitry layer 104. Thus, thepolarization of spatially pixilated portions of the incident light canbe individually modulated.

Alignment layers 114 and 118 provide a means of aligning the nematicliquid crystals of liquid crystal layer 116. This alignment isaccomplished by inducing a topographical asymmetry in the surfaces ofalignment layers 114 and 118, which controls the bulk orientation of theliquid crystals in the liquid crystal layer 116.

One known method for forming alignment layers includes forming apolyimide layer and then mechanically rubbing the polyimide layer in apredetermined direction to create the topographical asymmetry. Onecommon limitation of polyimide alignment layers is that they are notvery stable under high intensity and/or prolonged illumination. Indeed,after tens of hours of light stress, polyimide alignment layers candegrade enough to cause flares (e.g., unwanted lighter areas) in thedisplayed images. And, after several hundred hours of light stress, thedegradation is severe enough to cause permanent black areas in adisplayed white image and/or permanent white areas in a black image. Inother words, light stress will cause display devices having polyimidealignment layers to fail over time, resulting in diminished opticalperformance, costly warranty repairs/recalls, and/or lost customers.

To address the limitations of polyimide alignment layers, electron-beamevaporated thin film alignment layers were developed. These evaporatedalignment layers are formed by the oblique evaporation of silicondioxide (SiO₂). While such evaporated alignment layers have been foundto be stable under light stress, they have several drawbacks. First, thevacuum deposition method is both complicated and expensive, requiringsolid, high-purity SiO₂, a chamber held under high vacuum, and anelectron gun and power supply. Moreover, manufacturing throughput isalso very low due to the slow SiO₂ growth rate. These drawbacks resultin the display devices being more expensive to produce.

What is needed, therefore, is an efficient and inexpensive method forforming a robust alignment layer in an LCD device. What is also neededis an LCD device having alignment layer(s) that are stable afterprolonged light stress.

SUMMARY

The present invention overcomes the problems associated with the priorart by providing a novel method for forming the alignment layer(s) of aliquid crystal display device by annealing alignment layer material(e.g., spin-on dielectric) with laser light. Liquid crystal displaydevices of the invention include alignment layer(s) that are very stableunder prolonged, high-intensity light stress and that are easily andinexpensively manufactured with high throughput.

A method of forming an alignment layer of a display device according tothe invention includes the steps of providing a substrate having analignment layer material deposited thereon and applying light to thealignment layer material to alter a surface morphology of the alignmentlayer material. According to a particular method, the step of providinga substrate having an alignment layer material deposited thereonincludes depositing the alignment layer material over the substrateusing a spin-on process. The alignment layer material can include aspin-on dielectric (SOD) and, in particular, a SOD comprising silicondioxide (SiO₂).

In another particular method, the step of applying light to thealignment layer material includes applying a series of pulses from apulse laser to anneal portions of the alignment layer material. Theseries of pulses can be applied along a predetermined path with respectto the substrate, for example, by applying a predetermined number ofpulses (e.g., one) to the alignment layer material at a first locationalong the predetermined path to alter the surface morphology of thealignment layer material near the first location and then applying thepredetermined number of laser pulses to the alignment layer material ata second location along the predetermined path to alter the surfacemorphology of the alignment layer material near the second location. Inan even more particular method, the series of pulses is applied along aplurality of parallel paths and the parallel paths are defined such thatpulses applied to adjacent ones of the parallel paths overlap by apredetermined amount (e.g., approximately 50%).

The step of applying the series of laser pulses from the pulse lasercreates a repetitive pattern of features (e.g., a plurality ofgenerally-parallel valleys) on the surface of the alignment layermaterial. When the step of applying the series of pulses from the pulselaser includes applying a predetermined number of pulses at each of aplurality of predetermined locations, then a distance between adjacentones of the plurality of predetermined locations determines a pitchbetween adjacent ones of the features.

Regarding the step of providing a substrate, in one method the substratecomprises a silicon substrate and a plurality of pixel mirrors formed onthe silicon substrate, and the alignment layer material is depositedover the plurality of pixel mirrors. In another method, the substratecomprises a transparent substrate having a transparent electrode layerformed thereon, and the alignment layer material is deposited over thetransparent electrode layer.

A display device according to one embodiment of the invention includes asilicon substrate, a plurality of pixel mirrors formed over the siliconsubstrate, and an alignment layer formed over the plurality of pixelmirrors. The alignment layer includes an alignment surface opposite theplurality of pixel mirrors, and a surface morphology of the alignmentsurface includes a pattern of features formed therein that is indicativeof laser annealing. The pitch between adjacent ones of the features canbe approximately two micrometers and the roughness average (Ra) of thealignment surface can be between two and three nanometers. In aparticular embodiment, the pattern of features includes a pattern ofvalleys defined on the alignment surface where the density of a materialfrom which the alignment layer is formed is greater for areas associatedwith the valleys than for other areas of the alignment layer. Thealignment layer can be formed from a spin-on dielectric (SOD) and, inparticular, a SOD that comprises silicon dioxide.

The display device can further include a transparent substrate and aliquid crystal layer formed between the alignment layer and thetransparent substrate, where orientations of liquid crystals in theliquid crystal layer are controlled by the pattern of features. Thetransparent substrate can itself include a second alignment layer formedover the transparent substrate and the liquid crystal layer can beformed between the alignment layer and the second alignment layer. Insuch an embodiment, the second alignment layer of the transparentsubstrate can include a second alignment surface facing the liquidcrystal layer where a surface morphology of the second alignment surfaceincludes a second pattern of features that are indicative of the secondalignment surface having been laser annealed.

Another display device according to the present invention includes atransparent substrate, a transparent electrode layer formed over thetransparent substrate, and an alignment layer (e.g., a SOD) formed overthe transparent electrode layer. In such an embodiment, the alignmentlayer includes an alignment surface opposite the transparent electrodelayer, where a surface morphology of the alignment surface includes apattern of features formed therein that is indicative of laserannealing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the followingdrawings, wherein like reference numbers denote substantially similarelements:

FIG. 1 is a cross-sectional view showing a known liquid crystal displaydevice;

FIG. 2 is a top view showing a silicon wafer workpiece used formanufacturing liquid crystal display devices;

FIG. 3 is a top view of a transparent wafer workpiece used formanufacturing liquid crystal display devices;

FIG. 4A is a cross-sectional view showing a silicon wafer workpiece at afirst stage of a process for forming an alignment layer thereonaccording to the present invention;

FIG. 4B is a cross-sectional view showing a silicon wafer workpiece at asecond stage of a process for forming an alignment layer thereon;

FIG. 4C is a cross-sectional view showing a silicon wafer workpiece at athird stage of a process for forming an alignment layer thereon;

FIG. 5A is a cross-sectional view showing a transparent wafer workpieceat a first stage of a process for forming an alignment layer thereonaccording to the present invention;

FIG. 5B is a cross-sectional view showing a transparent wafer workpieceat a second stage of a process for forming an alignment layer thereon;

FIG. 5C is a cross-sectional view showing a transparent wafer workpieceat a third stage of a process for forming an alignment layer thereon;

FIG. 6 is a cross-sectional view showing a liquid display device havinglight-annealed alignment layers according to the present invention;

FIG. 7 is a micrograph image of an alignment layer formed by laserannealing according to the present invention;

FIG. 8 is a diagram showing an exemplary laser scan trace pattern forannealing an alignment layer material of the silicon wafer workpiece ofFIG. 4B and/or the transparent wafer workpiece of FIG. 5B;

FIG. 9 is a graph of an intensity profile for an exemplary laser beamused with the present invention;

FIG. 10 is a graph of the intensity profiles for three consecutivepulses of the laser beam of FIG. 9 at some point along the scan trace ofFIG. 8;

FIG. 11 is a flowchart summarizing one method for forming an alignmentlayer of a display device according to the present invention; and

FIG. 12 is a flowchart summarizing a particular method for performingthe third step (anneal alignment layer material) according to thepresent invention.

DETAILED DESCRIPTION

The present invention overcomes the problems associated with the priorart by providing a new method for forming the alignment layer(s) of aliquid crystal display device by annealing a spin-on dielectric withlaser light. Accordingly, the liquid crystal display devices of theinvention feature alignment layer(s) that are very stable underprolonged, high-intensity light stress and that are easily andinexpensively manufactured with high throughput. In the followingdescription, numerous specific details are set forth (e.g., particularlaser scan traces, laser specifics, etc.) in order to provide a thoroughunderstanding of the invention. Those skilled in the art will recognize,however, that the invention may be practiced apart from these specificdetails. In other instances, details of well-known wafer-processingpractices (e.g., spin-on processes, wafer preparation processes, etc.)and components (e.g., wafer processing apparatuses, etc.) have beenomitted, so as not to unnecessarily obscure the present invention.

FIG. 2 is a top view of an exemplary silicon wafer workpiece 200.Silicon wafer workpiece 200 is a processed silicon wafer which includesa silicon substrate 202 and a plurality of discrete imager chips 250formed on silicon substrate 202. As those skilled in the art willunderstand, each of imager chips 250 includes an array of pixel mirrors(not shown). Once silicon wafer workpiece 200 is diced, each of imagerchips 250 will be associated with a discrete liquid crystal on silicon(LCOS) display device.

FIG. 3 is a top view of an exemplary transparent wafer workpiece 300.Transparent wafer workpiece 300 includes a transparent substrate 302(e.g., a glass wafer), which can have various layers formed thereon aswill be described below. After processing, transparent wafer workpiece300 can be aligned with silicon wafer workpiece 200 and diced such thatportions of transparent wafer workpiece 300 will overlie respectiveimager chips 250, whereby liquid crystal material can be sandwichedtherebetween.

FIG. 4A is a cross-sectional view showing silicon wafer workpiece 200 ata first stage of a process for forming an alignment layer thereonaccording to the present invention. Accordingly, silicon wafer workpiece200 is denoted as workpiece 200A in FIG. 4A. Here, silicon waferworkpiece 200A is a processed silicon wafer that is ready to have aliquid crystal alignment layer formed thereon. In this embodiment,silicon wafer workpiece 200A includes a silicon substrate 202, at leastone integrated circuitry layer 204 formed over silicon substrate 202, aninsulating layer 206 formed over portions of integrated circuitry layer204, and a plurality of pixel mirrors 208. A planarized layer 210 and aprotective coating 212 are formed over the pixel mirrors 208. It shouldbe noted that the thicknesses of the layers and elements depicted inFIG. 4A (and in subsequent figures) are optimized for clarity and arenot drawn to scale.

The layers and elements of silicon wafer workpiece 200A are similar tothe corresponding layers and elements of FIG. 1 and, therefore, will notbe described again in detail. Moreover, silicon wafer workpiece 200A isexemplary in nature and can have additional or fewer layers and elements(e.g., additional insulating layers, etc.) than the ones shown.

FIG. 4B shows a second stage of forming an alignment layer according tothe present invention, which yields silicon wafer workpiece 200B. InFIG. 4B, an alignment layer material 214 is formed over workpiece 200Ain a deposition process. In a particular embodiment, alignment layermaterial 214 is a layer of spin-on dielectric (SOD), such asspin-on-glass (SOG) that is applied over protective coating 212 using aspin-on process. Even more particularly, SOD material 214 includessilicon dioxide (SiO₂), because SiO₂-based SOD is very resistant toprolonged light stress and will become denser with annealing. SODmaterial 214 can be applied at a thickness on the order of an opticalthin film.

After SOD material 214 is applied and hardened from its flowable form, atop surface 216 of SOD material 214 will have a particular morphology,which is shown representationally in FIG. 4B as being jagged. SODmaterial 214 will be laser annealed to change the morphology of topsurface 216 and form an alignment layer capable of aligning the liquidcrystals of a liquid crystal layer.

While alignment layer material 214 will be described as SOD containingSiO₂ herein, alignment layer material 214 can comprise other materialsthat are resistant to light stress and susceptible to laser annealing.Moreover, the processes shown in FIGS. 4A and 4B can be combined,whereby a processed silicon wafer workpiece 200B already havingalignment layer material 214 deposited thereon is provided, for example,where the SOD is applied by a different manufacturer.

FIG. 4C shows a third stage of forming an alignment layer according tothe present invention, which yields silicon wafer workpiece 200C. InFIG. 4C, SOD material 214 has been treated with light, which alters themorphology of top surface 216 and yields alignment layer 218. Inparticular, a series of laser pulses is applied to SOD material 214along a scan trace (FIG. 8) such that portions of SOD material 214 areannealed and densified. This annealing process changes the morphology ofportions of top surface 216 associated with the densified SOD material214 and thereby creates a first pattern of features 220, which arerepresented by the generally-parallel valleys 220 in FIG. 4C. Theportions of top surface 216 that are associated with the non-annealed(or lesser annealed) portions of SOD material 214 retain more of themorphology of top surface 216 prior to laser annealing and, therefore,define a second pattern of features 222 interposed between the firstpattern of features 220. Here, the second pattern of features 222 isshown as a plurality of generally-parallel ridges 222, which are locatedbetween the valleys 220. As indicated above, the annealing process makesthe SOD material 214 denser in areas associated with valleys 220compared with areas associated with ridges 222.

FIG. 5A is a cross-sectional view showing transparent wafer workpiece300 at a first stage of a process for forming an alignment layer thereonaccording to the present invention. Accordingly, transparent waferworkpiece 300 is denoted as transparent wafer workpiece 300A in FIG. 5A.In this first stage, a transparent wafer workpiece 300A is provided thatis ready to have a liquid crystal alignment layer formed thereon. Inthis example, transparent wafer workpiece 300A includes transparentsubstrate 302 and a transparent electrode layer 304 (e.g., indium tinoxide, ITO) formed on transparent substrate 302. Although not shown,transparent wafer workpiece 300A might also include other pre-formedlayers (e.g., anti-reflective coating(s), etc.).

FIG. 5B shows a second stage of forming an alignment layer according tothe present invention, which yields transparent wafer workpiece 300B. InFIG. 5B, an alignment layer material 306 is formed over transparentelectrode layer 304 in a deposition process. Like alignment layermaterial 214, alignment layer material 306 is an SiO₂-based SOD that isdeposited over transparent electrode layer 304 using a spin-on process.After SOD material 306 is applied and is hardened from its flowableform, a top surface 308 of SOD material 306 will have a particularmorphology, which is shown representationally in FIG. 5B as beingjagged. Like before, the processes shown in FIGS. 5A and 5B can becombined, whereby a processed transparent wafer workpiece 300B isprovided that already includes an alignment layer material 306 depositedthereon, for example, where the SOD is applied by a differentmanufacturer.

FIG. 5C shows a third stage of forming an alignment layer according tothe present invention, which yields transparent wafer workpiece 300C. InFIG. 5C, SOD material 306 has been treated with light, which alters themorphology of top surface 308 and yields alignment layer 310. Inparticular, a series of laser pulses is applied to SOD material 306along a scan trace (see FIG. 8) such that portions of SOD material 306are annealed and densified. The annealing process changes the morphologyof portions of top surface 308 associated with the densified SODmaterial 306 and thereby creates a first pattern of features 312, whichare represented by the generally-parallel valleys 312 in FIG. 5C. Theportions of top surface 308 that are associated with the non-annealed(or lesser annealed) portions of SOD material 306 retain more of themorphology of top surface 308 prior to laser annealing and, therefore,define a second pattern of features 314 interposed between the firstpattern of features 312. Here, the second pattern of features 314 isshown as a plurality of generally-parallel ridges 314, which are locatedbetween the valleys 312. As with workpiece 200C, the SOD material 306 isdenser in areas associated with valleys 312 than in areas associatedwith ridges 314.

FIG. 6 is a cross-sectional view of an assembled LCOS display device 600having laser-annealed alignment layers 218 and 310 according to thepresent invention. As shown in FIG. 6, display device 600 includes aportion of transparent wafer workpiece 300C, which has been inverted andpositioned over an associated portion of silicon wafer workpiece 200C,such that alignment layers 218 and 310 are facing each other. A liquidcrystal layer 602 is formed between the alignment layers 218 and 310.

As shown in FIG. 6, the altered surface morphologies of thelaser-annealed alignment layers 218 and 310 facilitate alignment of theliquid crystals of layer 602 based on the orientations of the valleys220 and 312 and the ridges 222 and 314 of alignment layers 218 and 310,respectively. Because alignment layers 218 and 310 are made from a SODincluding SiO₂, their surface morphologies are very robust and will notdegrade even after many hours of high-intensity light stress. Theinvention, therefore, provides this very important advantage over priorart displays that use organic (e.g., polyimide) alignment layers.Moreover, because the SOD used in layers 218 and 310 is applied with aspin-on process, the invention facilitates the application of alignmentlayer material much more quickly, simply, and less expensively thanprior art evaporation deposition methods. The laser annealing process isalso faster, simpler, and cheaper than prior art evaporation depositionmethods. Accordingly, the invention facilitates production of alignmentlayers that have high longevity at a reduced cost, while significantlyincreasing wafer throughput and device production.

It will be understood that liquid crystal display device 600 can includeadditional, fewer, or alternative elements (e.g., a gasket surroundingliquid crystal layer 602, anti-reflective coatings, etc.) as those shownin FIG. 6. Additionally, the orientations of alignment layers 218 and310 with respect to each other can be altered, for example, depending onthe rotational orientations of the substrates 200C and 300C when coupledtogether.

FIG. 7 is a micrograph image 700 of alignment layer 218 (oralternatively alignment layer 310) that has been formed by laserannealing according to the present invention. As shown in image 700,alignment layer 218 includes the first pattern of features 220 and thesecond pattern of features 222. Features 220 correspond with theannealed portions of alignment layer 218 and are associated with denserSOD material 214, and features 222 correspond with the non-annealed (orlesser annealed) portions of SOD material 214 that are less dense. InFIG. 7, the first pattern of features 220 is shown as a pattern ofgenerally-parallel valleys 220 and the second pattern of features 222 isshown as a pattern of generally-parallel ridges 222.

The alternating nature of the valleys 220 and ridges 222 give alignmentlayer 218 a consistent, striped form. In this embodiment, the pitchbetween valleys 220 is approximately two to two-and-a-half micrometers(2.0-2.5 μm). However, this pitch can be adjusted as desired, forexample, to obtain a predetermined number of valleys 220 (or ridges 222)per pixel of the display device.

FIG. 7 also provides other information about the surface morphology ofalignment layer 218. For example, FIG. 7 indicates that the roughnessaverage (Ra) of the annealed surface of alignment layer 218 isapproximately 2.5 nanometers. Furthermore, FIG. 7 shows that thelocations of valleys 220 and ridges 222 alternate along the direction ofa scan trace that is traversed during the laser-annealing process ofalignment layer 218. In this embodiment, the long direction of valleys220 and ridges 222 is shown as being generally perpendicular to the scandirection. In other embodiments, the long direction of valleys 220 andridges 222 can be oblique or even parallel to the direction of the scantrace.

It should also be noted that the first pattern of features 220 and thesecond pattern of features 222 of annealed alignment layer 218 aredescribed herein as patterns of “valleys” and “ridges” for convenience.Accordingly, this terminology should not be construed in such a way thatlimits the scope of the invention. For example, in some instances or atsome locations, a feature characterized as a ridge or part of a ridgemight have portions with a lower elevation than a feature characterizedas a valley or part of a valley. As another example, the patterns offeatures 220 and 222 might also be characterized as flattened portions220 and jagged portions 222, respectively. Importantly, the patterns offeatures 220 and 222 shown in FIG. 7 are intended to illustrate that thelaser-annealing process of the invention alters the surface morphologyof the alignment layer material 214 in some desirable way such that theannealed alignment layer material 214 will function as a liquid crystalalignment layer 218 in a liquid crystal display device. Moreparticularly, an alignment layer of the invention has an altered surfacemorphology with patterns of features that are defined in part by a laserscan trace (see FIG. 8). In turn, the orientations of the liquidcrystals in the liquid crystal layer are aligned and controlled (e.g.,restrained) by these features also according to the laser scan trace.

FIG. 8 is a diagram showing an exemplary laser scan trace 800 alongwhich a series of pulses of a laser beam 802 are applied to SOD material214 to produce laser-annealed alignment layer 218 according to thepresent invention. While scan trace 800 is described with reference tosilicon wafer workpiece 200B, scan trace 800 can also be used to annealSOD material 306 of transparent wafer workpiece 300B.

As shown in FIG. 8, scan trace 800 comprises a plurality of parallelhorizontal paths 806-818. A pulse laser (not shown) applies a series ofpulses of laser beam 802 to SOD material 214 in a back-and-forth manneralong these horizontal paths 806-818. Left-to-right horizontal paths806, 810, 814, and 818 of scan trace 800 are indicated by long-dashedlines, whereas right-to-left horizontal paths 808, 812, and 816 of scantrace 800 are indicated with short-dashed lines.

Pulses of laser beam 802 are applied to SOD material 214 from left toright across silicon wafer workpiece 200B along horizontal path 806.Once across silicon wafer workpiece 200B, the laser aperture (e.g., beamslit, not shown) is repositioned with respect to silicon wafer workpiece200B to the beginning of horizontal path 808. Then, pulses from laserbeam 802 are applied to SOD material 214 from right to left acrosssilicon wafer workpiece 200B along horizontal path 808. Once acrosssilicon wafer workpiece 200B, the laser aperture is repositioned withrespect to silicon wafer workpiece 200B to the beginning of horizontalpath 810. Thereafter, pulses of a laser beam 802 are applied to SODmaterial 214 from left to right along horizontal path 810. Once acrosssilicon wafer workpiece 200B, the laser aperture is repositioned withrespect to silicon wafer workpiece 200B to the beginning of horizontalpath 812. Thereafter, pulses from laser beam 802 are applied to SODmaterial 214 from right to left along horizontal path 812, and so onuntil scan trace 800 is complete.

Once laser annealing is completed, silicon wafer workpiece 200C willhave been created and will have an alignment layer 218 with an alteredsurface morphology sufficient to align the liquid crystals of layer 602.Referring back to FIG. 7, scan trace 800 yields a first pattern offeature 220 and a second pattern of features 222 that follow (alternatealong) the scan directions of horizontal paths 806-818. In turn, becausethe liquid crystals in the liquid crystal layer 602 are alignedaccording to the orientations of the features 220 and 222, the alignmentof the liquid crystals is also based at least in part on the laser scantrace.

In the present embodiment, laser beam 802 is rectangular in shape (e.g.,27 mm×6 μm) and pulses are applied to SOD material 214 with the longdirection of laser beam 802 oriented generally perpendicularly to thescan directions along horizontal paths 806-818. However, other laserbeam orientations (e.g., obliquely, parallel, etc.) with respect to scandirection of the trace can be used. It should also be understood thatscan trace 800 can be completed either by moving silicon wafer workpiece200B relative to the aperture producing laser beam 802 or by moving thelaser beam 802 (e.g., mechanically or optically) relative to siliconwafer workpiece 200B.

FIG. 8 also shows that each subsequent horizontal path overlaps with theprior horizontal path by a predetermined amount, which in thisembodiment is approximately 50%. For example, horizontal path 808overlaps horizontal path 806 by approximately 50%, horizontal path 810overlaps horizontal path 808 by approximately 50%, and so on.Accordingly, the pulses from laser beam 802 applied along one horizontalpath will also overlap pulses applied along the prior horizontal path bythe predetermined amount. The overlap ensures that the patterns offeatures (e.g., valleys 220 and ridges 222) of the resulting alignmentlayer 218 are well-defined after laser annealing. While 50% overlap isused in FIG. 8, other overlaps (e.g., 40%, 60%, etc.) can be used. Asanother option, trace 800 can include additional horizontal paths at thetop and bottom of silicon wafer 202 to ensure overlap coverage of thetop half of horizontal path 806 and the bottom half of horizontal path818.

The scan trace 800 and laser beam 802 shown in FIG. 8 are exemplary innature. It should, therefore, be understood that other scan traces andlaser beam geometries can be used as desired. For example, if a laserbeam extending the full diameter of the wafer 200B in the vertical (y)direction is used, then fewer (e.g., only one) horizontal pass(es) wouldbe needed. At the other extreme, if a small, round spot beam was used,then the scan trace would include many more horizontal passes. As yetanother example, laser pulses could be applied along vertical or obliquepaths. As still another example, the long-direction of laser beam 802could be oriented parallel or obliquely to the paths of the scan trace,as mentioned above. These and other alternatives will be apparent inview of this disclosure.

It should also be noted that the horizontal paths 806-818 in FIG. 8 areshown to extend way beyond the limits of wafer 200B for clarity.However, it will be understood that pulses from laser beam 802 do notneed to be applied beyond the limits of wafer 200B and/or do not need tobe applied where annealing of alignment layer 214 is not necessary.

FIG. 9 is a graph of an intensity profile 900 along the width of theshort direction of laser beam 802. Pulse width (in micrometers, μm) isshown along the horizontal axis 902, whereas intensity as a percentageof full intensity (%) is shown along vertical axis 904. As shown, laserbeam 802 has a Gaussian intensity distribution along its pulse width. Acommon statistical reference used to characterize Gaussian pulse widthis “full width at half maximum” (FWHM). FWHM refers to the full width ofthe laser beam 802 measured at half (50%) its maximum intensity. In thisexample, laser beam 802 has a pulse width of 6 μm at FWHM.

In a particular embodiment, a laser beam 802 having a width of sixmicrometers (6 μm) at FWHM can be used to anneal alignment layers 218and 310. Such a laser beam 802 can also have a wavelength in the greenregion of the spectrum (e.g., 515 nm), a pulse duration of 300-500nanoseconds (ns), and an energy density of 0.5-3.0 Joules per squarecentimeter (J/cm²) to facilitate annealing. At these specifications, alinear scan rate of approximately 20 mm per second at a laser pulse rateof 10 kilohertz (kHz) is possible if the laser beam is moved by twomicrometers (2 μm) between each pulse.

FIG. 10 is a graph of intensity profiles for three consecutive pulses oflaser beam 802, which are applied to anneal SOD material 214 at somearbitrary location along horizontal path 806 of scan trace 800 shown inFIG. 8. Location (in μm) along horizontal path 806 is shown alonghorizontal axis 1002, whereas intensity of each pulse of laser beam 802as a percentage of full intensity (%) is shown along vertical axis 1004.Like in FIG. 9, the intensity profiles are shown for the width (e.g.,the 6 μm dimension) of laser beam 802. While FIG. 10 will be describedwith respect to SOD material 214, the following description is alsoapplicable to SOD material 306 of transparent wafer workpiece 300B.

A first pulse 1006 of laser beam 802 (shown in solid) is applied to SODmaterial 214 with its intensity peak at a first location (x=2 μm in thisexample) along horizontal path 806. The silicon wafer workpiece 200Band/or the position of the laser beam 802 is then moved by apredetermined amount such that laser beam 802 targets a second locationalong horizontal path 806. Then a second pulse 1008 of laser beam 802(shown in long dashes) is applied to SOD material 214 with its intensitypeak at the second location (x=4 μm in this example). The silicon waferworkpiece 200B and/or the position of the laser beam 802 is then movedby the predetermined amount to a third location along horizontal path806. There, a third pulse 1010 of laser beam 802 (shown in short dashes)is applied to SOD material 214 with its intensity peak at the thirdlocation (x=6 μm in this example).

The predetermined distance between consecutive laser pulses has been setat 2 micrometers in this example. Accordingly, a pulse of laser beam 802is applied every two micrometers along horizontal path 806 of scan trace800. Thereafter, pulses are applied at the predetermined distance alongeach consecutive horizontal path 808-818 until scan trace 800 iscomplete. However the pulse locations move from right to left forhorizontal paths 808, 812, and 816.

The energy delivered to SOD material 214 by the series of pulses oflaser beam 802 anneals SOD material 214 and, thereby, creates the firstpattern of features (valleys) 220 and the second pattern of features(ridges) 222 shown in FIG. 7. Additionally, the pitch between locationswhere laser pulses (e.g., pulses 1006, 1008, and 1010) are applieddetermines the pitch between the features of alignment layer 218. Forexample, if the pitch between the locations of where laser pulses areapplied changes, then the pitch between valleys 220, as well as thepitch between ridges 222, will also change. Changing the pitch isdesirable, for example, to ensure that a particular number of features(e.g., valleys) are located over each pixel in a pixel array. Thelocation of valleys 220 of alignment layer 218 will generally correspondto the locations of the intensity peaks of the laser pulses 1006, 1008,and 1010. In this example, the valleys 220 would be located atapproximately x=2 μm, x=4 μm, x=6 μm, etc. and have a pitch ofapproximately 2 μm. However, pitches of above 10 μm and below 0.2 μm arepossible.

In the above example, one pulse of laser beam 802 is applied at eachlocation along the horizontal paths 806-818. However, in some cases itmight be desirable to apply multiple pulses of laser beam 802 at eachlocation, for example, for lower powered lasers or where more energyneeds to be delivered to change the surface morphology of the alignmentlayer material 214.

Methods of the present invention will now be described with reference toFIGS. 11-12. For the sake of clear explanation, these methods might bedescribed with reference to particular elements of thepreviously-described embodiments. However, it should be noted that otherelements, whether explicitly described herein or created in view of thepresent disclosure, could be substituted for those cited withoutdeparting from the scope of the present invention. Therefore, it shouldbe understood that the methods of the present invention are not limitedto any particular elements that perform any particular functions.Furthermore, some steps of the methods presented herein need notnecessarily occur in the order shown. For example, in some cases two ormore method steps may occur simultaneously. These and other variationsof the methods disclosed herein will be readily apparent, especially inview of the description of the present invention provided previouslyherein, and are considered to be within the full scope of the invention.

FIG. 11 is a flowchart summarizing one method 1100 for forming analignment layer of a display device according to the present invention.In a first step 1102, a processed substrate used in the manufacture ofone or more display devices (e.g., silicon wafer workpiece 200A,transparent wafer workpiece 300A) is provided. In a second step 1104, analignment layer material (e.g., SOD including SiO₂) is deposited overthe substrate, for example, using a spin-on process. Then, in a thirdstep 1106, light (e.g., a series of pulses 1006-1010 from a pulse laser)is applied to the alignment layer material to alter its surfacemorphology sufficiently for the annealed alignment layer material tofacilitate alignment of the liquid crystals of a subsequently formedliquid crystal layer.

FIG. 12 is a flowchart summarizing a method for performing step 1106(anneal alignment layer material with light) of method 1100. In a firststep 1202, the processed substrate is optionally loaded into awafer-processing apparatus and undergoes any desirable initial alignmentand calibration procedure(s) (e.g., locating the wafer with respect tothe laser aperture, etc.). Then, in a second step 1204, a firstpredetermined position over the processed substrate for applying thelaser beam is targeted, for example, by moving the substrate, moving theaperture of the pulse laser, adjusting an optical system that directsthe laser beam from the pulse laser, etc. Then, in a third step 1206, apredetermined number of laser pulse(s) (e.g., one, etc.) is applied tothe alignment layer material of the substrate at the first predeterminedposition. Then, in a fourth step 1208, a check is made to determine ifthe end of a current path (e.g., horizontal path 806) of the laser scantrace (e.g., scan trace 800) has been reached. If not, then in a fifthstep 1210, a next predetermined position over the processed substrate istargeted (e.g., by moving the target location by 2 μm) and the methodreturns to step 1206 such that the predetermined number of laser pulsesis applied to the alignment layer material at the next position.

However, if in step 1208, it is determined that the end of the currentpath of the laser scan trace has been reached, then the method continuesto a sixth step 1212. In sixth step 1212, it is determined if anotherpath (e.g., horizontal path 808) in the scan trace needs to be traversedand annealed. If yes, then in a seventh step 1214, the next path istargeted to provide a predetermined overlap (e.g., 50%) with respect tothe prior path. Then, method 1106 proceeds to second step 1204 where thefirst predetermined location of the next path is targeted. If, however,in step 1212, it is determined that no additional path needs to beannealed (e.g., the full scan trace is complete), then method 1106 endsand the substrate can optionally be removed from the wafer processingapparatus.

The description of particular embodiments of the present invention isnow complete. Many of the described features may be substituted, alteredor omitted without departing from the scope of the invention. Forexample, alternate laser scan traces (e.g., vertical) and laser beamdimensions, may be substituted for the laser scan trace 800 and laserbeam 802. As another example, other desirable patterns of features canbe laser annealed into the surfaces of the alignment layers in place ofthe striped features 220 and 222 that are shown. These and otherdeviations from the particular embodiments shown will be apparent tothose skilled in the art, particularly in view of the foregoingdisclosure.

We claim:
 1. A method of forming an alignment layer of a display device,said method comprising: providing a substrate having an alignment layermaterial deposited thereon; and applying light to said alignment layermaterial; said step of applying light alters a surface morphology of asurface of said alignment layer material; and wherein said step ofapplying light to said alignment layer material includes applying aseries of pulses from a pulse laser to anneal portions of said alignmentlayer material; and said alignment layer material includes an oxide. 2.The method of claim 1, wherein said series of pulses is applied along apredetermined path with respect to said substrate.
 3. The method ofclaim 2, further comprising: applying a predetermined number of pulsesto said alignment layer material at a first location along saidpredetermined path to alter said surface morphology of said alignmentlayer material near said first location; and applying said predeterminednumber of laser pulses to said alignment layer material at a secondlocation along said predetermined path to alter said surface morphologyof said alignment layer material near said second location.
 4. Themethod of claim 3, wherein said predetermined number is one.
 5. Themethod of claim 2, wherein: said series of pulses is applied along aplurality of parallel paths; and said parallel paths are defined suchthat exposure areas of adjacent ones of said parallel paths overlap by apredetermined amount.
 6. The method of claim 5, wherein saidpredetermined amount is approximately 50%.
 7. The method of claim 1,wherein said step of applying said series of laser pulses from saidpulse laser creates a repetitive pattern of features on said surface ofsaid alignment layer material.
 8. The method of claim 7, wherein: saidstep of applying said series of pulses from said pulse laser includesapplying a predetermined number of pulses at each of a plurality ofpredetermined locations; and a distance between adjacent ones of saidplurality of predetermined locations determines a pitch between adjacentones of said features.
 9. The method of claim 7, wherein said pattern offeatures comprises a plurality of generally-parallel valleys.
 10. Themethod of claim 1, wherein said alignment layer material comprisesspin-on dielectric (SOD).
 11. The method of claim 10, wherein said SODcomprises silicon dioxide.
 12. The method of claim 1, wherein said stepof providing said substrate includes depositing said alignment layermaterial over said substrate using a spin-on process.
 13. The method ofclaim 12, wherein said alignment layer material comprises spin-ondielectric (SOD).
 14. The method of claim 1, wherein: said substratecomprises a silicon substrate and a plurality of pixel mirrors formed onsaid silicon substrate; and said alignment layer material is depositedover said plurality of pixel mirrors.
 15. The method of claim 1,wherein: said substrate comprises a transparent substrate having atransparent electrode layer formed thereon; and said alignment layermaterial is deposited over said transparent electrode layer.
 16. Adisplay device comprising: a silicon substrate; a plurality of pixelmirrors formed over said silicon substrate; and an alignment layerformed over said plurality of pixel mirrors; and wherein said alignmentlayer includes an alignment surface opposite said plurality of pixelmirrors; and a surface morphology of said alignment surface includes apattern of features formed therein, said pattern of features beingindicative of laser annealing; and wherein said alignment layer includesan oxide.
 17. The display device of claim 16, wherein said pattern offeatures includes a pattern of valleys defined on said alignmentsurface.
 18. The display device of claim 17, wherein the density of amaterial from which said alignment layer is formed is greater for areasassociated with said valleys than for other areas of said alignmentlayer.
 19. The display device of claim 16, wherein said alignment layercomprises a spin-on dielectric (SOD).
 20. The display device of claim19, wherein said SOD comprises silicon dioxide.
 21. The display deviceof claim 16, further comprising: a transparent substrate; a liquidcrystal layer formed between said alignment layer and said transparentsubstrate; and wherein orientations of liquid crystals in said liquidcrystal layer are controlled by said pattern of features.
 22. Thedisplay device of claim 16, further comprising: a transparent substrate;a second alignment layer formed over said transparent substrate; and aliquid crystal layer formed between said alignment layer and said secondalignment layer; and wherein said second alignment layer includes asecond alignment surface facing said liquid crystal layer; and a surfacemorphology of said second alignment surface includes a second pattern offeatures formed therein, said second pattern of features beingindicative of laser annealing.
 23. A display device comprising: atransparent substrate; a transparent electrode layer formed over saidtransparent substrate; and an oxide alignment layer formed over saidtransparent electrode layer; and wherein said oxide alignment layerincludes an alignment surface opposite said transparent electrode layer;and a surface morphology of said alignment surface includes a pattern offeatures formed therein, said pattern of features being indicative oflaser annealing.
 24. The display device of claim 23, wherein said oxidealignment layer comprises a spin-on dielectric.